1. Field of the Invention: The present invention relates to the field of fluid shear couplings, and particularly to a coupling of the type used as a vehicle fan drive in which a rotor is received within a driven member.
2. Description of the Prior Art: A variety of fluid shear couplings, also referred to as viscous couplings, have been proposed in the prior art. Many of these couplings include a rotor which is connectable with an external drive source and is received within a housing that defines a fluid shear chamber. Improvements for such couplings have been proposed along many lines including bearing structures, fluid valving, temperature controls and torque transfer. A purpose behind most improvements in fluid shear couplings is the achievement of a coupling which operates efficiently with a minimum of cost and weight. The present invention satisfies all of these conditions.
In the preferred embodiment, the present invention provides a fluid shear coupling which includes interdigitated ridges and grooves to increase the transmission of torque between the rotor and the driven housing. This general feature is disclosed in a number of patents, many of which appear in class 192, subclass 58. Examples of patents which disclose interdigitated ridges and grooves are the following: U.S. Pat. Nos. 3,856,122, issued to Leichliter on Dec. 24, 1974; 3,323,623, issued to Roper on June 6, 1967; and 3,809,197, issued to Clancey on May 7, 1974.
The present invention also provides a unique sealing structure for a temperature-responsive fluid valve. General valving structures are well known in the art and typically assume two forms. One type of valve structure utilizes a valve which is spring-biased to pivot outwardly from a fluid aperture when a control pin is displaced to permit such pivoting. Examples of such valve structures are disclosed in U.S. Pat. Nos. 4,090,596, issued to Blair on May 23, 1978; 4,086,990, issued to Spence on May 2, 1978; 4,036,339, issued to Kikuchi on July 19, 1977; and 3,964,582, issued to Mitchell on June 22, 1976. In each of these patents, the pin slides through a hole in the cover of the coupling. A sealing member is inserted into an annular groove on the inside or fluid side of the cover to seal the sliding control pin. A second type of fluid control valve is one which is rotated to or from the fluid flow aperture, typically in correspondence with a coiled, temperature-sensitive spring. Examples of other types of such valve structures are contained in U.S. Pat. Nos. 4,062,432, issued to Evans on Dec. 13, 1977, and 3,191,733, issued to Weir on June 29, 1965.
Another feature of the present invention is contained in the method and structure for coupling the cover and bearing housing of the apparatus. One of the conventional methods for securing a cover to a bearing housing is by simply bolting the members together. The bolts are typically received through flanges which extend outwardly from the central portion of the coupling at which the shear surfaces are located. This method typically requires the inclusion of a substantial outer flange having a width, along a diameter, of sufficient distance to accommodate the several bolts. A disadvantage of this approach is that the amount and location of such a flange significantly increases the weight of the coupling apparatus and also places that weight at the outer perimeter at which the moment of inertia is the greatest. Also, the method is relatively slow to perform.
A second alternative in the prior art has been to provide either the bearing housing or the cover with a perimetric flange which is then rolled over the edge of the other member to join them together. Examples of this construction are contained in U.S. Pat. Nos. 3,011,607, issued to Englander on Dec. 5, 1961 and 3,007,560, issued to Weir on Nov. 7, 1961. This approach is also shown in the Leichliter, Roper and Clancey patents previously identified. Disadvantages of this procedure include a resultant distortion of the cover faces, and also the slowness of the process.
A further aspect of the present invention relates to the formation, particularly by casting, of certain components of a fluid shear coupling, especially using magnesium or a magnesium alloy. Materials which have conventionally been used in formation of the cover, bearing housing and rotor for prior art devices have included various steel and aluminum compositions. Applicant is not aware, however, of the use of a magnesium alloy for this purpose. A further aspect of the present invention is the inclusion of a plate which defines the several annular ridges and grooves for the driven member of a fluid shear coupling, which plate is mounted to the cover member of the coupling. In the prior art, for those devices which utilize a driven member having annular ridges and grooves, these elements are provided as integral portions of the cover.